economics: the responsiveness of demand to price where a large drop in demand for a small increase in price is considered elastic and a small drop in demand for a large increase in price is considered inelastic

Measured mathematically as the percentage change in the quantity demanded of a product, divided by the percentage change in the price charged. Elasticity is relative, but generally, if a 1% price increase results in less than a 1% drop in demand, the demand curve might be described as inelastic.